1. Technical Field
This invention relates to heat treating of large parts such as steel rings and bearing races that require the parts to be heated and then quenched to impart case hardening. Such case hardening typically requires a two step process, gas carburizing and austenitizing. For gas carburizing, a steel part is heated to an elevated uniform temperature in a carbon-rich gas atmosphere. This allows the carbon in the atmosphere to diffuse into a layer at the surface of the part.
During austenitizing (heat treating), a steel part is heated within the austenitizing range 1,455-1,680°, Fahrenheit, in a gas-fired integrated quenching furnace. The heated part is heated to a uniform temperature and then rapidly quenched in a medium, typically oil. This heating and rapid cooling imparts dimensional variations in such large parts and they will become out-of-round and out-of-flat, requiring the need initially to have extra stock in the part to be machined off and extra case depths to ensure sufficient case after machining.
2. Description of Prior Art
Prior art quenching methods and apparatus can be seen generally in U.S. Pat. Nos. 6,048,418; 8,034,258 B2; and EP 1,191,111 A1.
U.S. Pat. No. 6,048,418 is directed to a ring-forming apparatus and heat treating process wherein flat ring parts are heated, then placed in a die and submerged in a quenching bath to form the ring into its final shape while therewithin.
U.S. Pat. No. 8,034,285 B2 illustrates quenching methods and devices for quenching a steel ring which includes a corresponding set of quenching dies, a die handling tool, and related methods to lift the corresponding set of quenching dies and die handling apparatus to load and unload the dies into a quenching press.
Finally, Patent EP 1,191,111 A1 discloses a method and apparatus for press tempering wherein a heated part is placed into a pressing device and then cooled with a coolant.